-LRB- CNN -RRB- -- Call it a meteorological mystery : Forecasters warned that there would be at least six Atlantic hurricanes this season , but so far we 've seen only one .

It 's the first year in recent memory that every major hurricane forecast has busted after pointing to `` above normal activity . ''

We are passing the season 's halfway point . Normally , the Atlantic would see its first hurricane by August 10 , and a major hurricane -LRB- Category 3 or higher -RRB- by September 4 .

But this year is not normal .

2013 's first hurricane -- Humberto -- was a month late . It was so behind schedule it nearly set a record for tardiness .

Although the number of 2013 Atlantic storms is above average -- at nine so far -- the intensity of those storms has n't matched the forecasts . Humberto -- a Category 1 with winds under 95 mph -- ranked nowhere close to a major hurricane when it spun out harmlessly in the mid-Atlantic .

What 's going on here ? Climate change ? El Niño ? Something else ?

Experts do n't have a full understanding , but three things are getting the blame :

-- In the eastern Atlantic , where hurricanes are often born , African desert air is drying the moisture that hurricanes need to form .

-- In the western Atlantic and Gulf of Mexico , fast horizontal winds have been cutting off the tops of potential hurricanes , sapping their power .

-- Experts speculate that dry air from Brazil 's drought may be another factor .

Chad Myers explains this strange hurricane season

Respected veteran hurricane scientist Bill Gray of Colorado State University has pretty much given up for this year .

His research group predicted eight hurricanes this season . `` The forecast up to now is a bust , '' says Gray . `` The second half of the season will be more active , '' he predicts , with as many as five more hurricanes . Even with the most sophisticated prediction techniques , Gray says , `` there 's still 40 or 50 % of variations in tropical storm and hurricane activity that we ca n't explain . ''

Poking fun at his government rivals , Gray jokes about `` reports of a suicide watch '' among the meteorologists who worked on this year 's National Weather Service forecast . Nonetheless , the feds are standing firm .

Unlike Gray , they 're not ready to cry uncle .

`` Our forecast remains the same , '' weather service spokesman Chris Vaccaro said . `` We 're sticking by it . ''

The NWS -- last May -- initially forecast 13 to 20 `` named storms , '' including seven to 11 hurricanes . Then in August , it dialed down that initial forecast to predict 13 to 19 named storms , including six to nine hurricanes .

So far , including Humberto , we 've seen nine named storms . From the weather service 's perspective , that statistic shows its forecast remains valid .

`` In some ways we 're ahead of schedule , '' says Vaccaro . `` And in late September and October there 's plenty of time for the number of tropical storms and hurricanes to climb . '' According to the weather service forecast , at least four more tropical storms or hurricanes will form in the next 11 weeks . That 's 77 days , or one storm forming every 19 days .

It would be a mistake to believe that the second half of any hurricane season would resemble the first half , says Vaccaro , who stresses that we 're not experiencing a `` lull . '' `` Historically speaking , June and July and the first part of August are typically fairly quiet , '' he says . September , he warns , is the time when storms can start to get get serious .

Some key examples :

- Hurricane Gloria hit the eastern United States in September 1985 .

- In 1938 a disastrous hurricane tore up parts of the northeast , also during the month of September .

- In 1998 one of the deadliest storms on record , Hurricane Mitch , raked the Caribbean and Central America after forming in late October .

- Hurricane Sandy , which altered so many lives last year when it slammed into much of the Eastern Seaboard , did n't appear until October .

- Although Andrew devastated South Florida in late August , it was the first hurricane of 1992 , a season that overall turned out to be below normal .

- In 2002 , Gustav , the first hurricane of the season , did n't occur until September . Weeks later in early October , Hurricane Lili made a destructive landfall along the Louisiana coast .

There 's also always the possibility of a freak storm after the season ends , says Vaccaro . `` Nature sometimes throws us a curve ball as it has in the past when we 've seen storms develop in the month of December . ''

How likely is it that the weather service forecast will pan out ? In this crazy year , it 's anybody 's guess .

Hurricane watchers point out that there are more signs that something may be amiss :

-- The Accumulated Cyclone Energy index -- a rating system that compares the intensity of storm seasons -- would normally be around 55 for the Atlantic . It 's now a paltry 16 . Globally the rating is a stunning 255 , roughly half of what we should see this time of year .

-- When an ocean basin kicks up a fuss on one part of the globe , usually another ocean basin is quiet . Nature tends to balance itself that way . This year , according to the ratings , storm activity in all the world 's ocean basins is below normal . This adds even more to the mystery .

-- This year there is no El Niño , which would keep the season quiet , or La Niña , which would fuel a more active season . Atlantic surface temperatures continue to be above normal , which also would help stir up storms .

-- Climate change ? As you might expect , opinions differ . Some researchers say global warming from the buildup of CO2 carbon gas pollution in the atmosphere will lead to more frequent and more powerful hurricanes . Some studies support that hypothesis , while others are less convinced . Although scientists are 95 % sure that CO2 is warming the globe , they 're not certain about how that affects hurricanes . `` There are mixed signals , '' says Vaccaro . `` So the jury 's still out and research is ongoing . ''

Related : Silent hurricane season fuels debate over global warming

At the National Hurricane Center in Miami , they 're comparing this year to `` a slow first half of a slow football game , '' says hurricane center spokesman Dennis Feltgen .

`` It really does n't matter how many storms form out there , '' Feltgen says . `` If one gets to you , it 's a bad year . ''

The news media is n't making too much of this strange season , he says .

But he warns , do n't be fooled by it . Be prepared .

The mystery has grabbed the attention of Gray and other scientists , who are looking forward to analyzing all the data . Who knows ? We may learn a few things .

`` We 'll figure it out , '' says Gray . `` Let 's see what the rest of the season brings . ''

CNN Meteorologist Chad Myers and producer Sean Morris contributed to this report .

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Number of 2013 Atlantic storms is above average , but intensity has n't matched forecasts

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Halfway into season , Atlantic has only seen one hurricane -- a weak one named Humberto

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Weather service stands by forecast for 13 `` named storms , '' including 6 hurricanes

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Experts were surprised by hurricane-killing dry African air and high Gulf winds